| In October of 1999, Nichia Corporation of Japan launched the commercial sale of their InGaN-based violet diode laser. Operating near 400 nm with an output power of 5 mW, this laser presents numerous opportunities for laser induced fluorescence detection (LIF) in capillary electrophoresis (CE). The laser offers significant advantages over conventional red diode lasers and fills a void in the 400-nm region of the electromagnetic spectrum where a suitable laser line for LIF detection had not been available.; To demonstrate the suitability of the violet diode laser for LIF detection in CE, amino acids labeled with the common fluorogenic probe naphthalene-2,3-dicarboxaldehyde were chosen as test compounds. Detection limits of 3–8 nM were achieved with a commercial instrument and over 10-fold lower using a home-built LIF detector. This sensitivity is comparable to that achieved previously with the HeCd laser, making the violet diode laser an attractive alternative for this application.; Exploiting the high stability of diode lasers and the numerous fluorescent probes that excite near 400 nm, the violet diode laser was evaluated for indirect LIF detection. Inorganic anions were determined using 8-hydroxypyrene-1,3,6-trisulfonic acid as the indirect detection probe with limits of detection ranging from 0.4–0.6 μM. A series of phosphonic acids were detected using tetrakis-(4-sulphophenyl)porphine as the indirect detection probe and detection limits of 0.2 μM were achieved. Baseline stability observed with the violet diode laser was excellent, with dynamic reserve values greater than 1000.; The highly intense Soret excitation band of porphyrins near 400 nm makes them an ideal target for sensitive detection using the violet diode laser. A limit of detection of 20 pM was achieved for urinary porphyrins, which represents a gain in sensitivity of more than two orders of magnitude over previously reported values. This high sensitivity allowed for up to a 100-fold dilution of urine prior to analysis, compared to the pre-concentration steps required in previously reported methods.; Exploiting its high sensitivity for porphyrins, the violet diode laser was used for LIF detection of porphyrin-containing or ‘heme’ proteins. After reconstitution with a more fluorescent porphyrin, the limit of detection for myoglobin was 1 nM. |
